The disclosure relates generally to toner additives, and in particular, toner additives that provide desired higher toner charge and low relative humidity (RH) sensitivity. The toner additives comprise titania nanotubes or titania nanosheets in combination with or in place of the commonly used anatase or rutile crystalline titania.
Toners can comprise at least a binder resin, a colorant and one or more external surface additives. The external surface additives can be added in small amounts. Examples of external surface additives include, for example, silica, titanium dioxide, zinc stearate and the like. The properties of a toner are influenced by the materials and amounts of the materials of the toner. The charging characteristics of a toner also can depend on the carrier used in a developer composition, such as, the carrier coating.
Toners having triboelectric charge within the range of about −30 μC/g to about −45 μC/g may be achieved by including smaller-sized silica particles as external additives, for example silica particles having average sizes of less than about 20 nm, such as, for example, R805 (˜12 nm) and/or R972 (˜16 nm) (Evonik, N.J.). However, developability at areas of low toner area coverage degrades over time. That has been attributed to the smaller-sized additives being impacted into the toner surface over time. The problem with smaller-sized additives may be addressed by using larger-sized additives, i.e., additives having a size of about 40 nm or larger such as, for example, RX50 silica, RX515H silica or SMT5103 titania (Evonik, N.J.). However, such toners do not exhibit as high a triboelectric charge and also exhibit charge through.
Thus, there remain problems with providing high charge with good relative humidity (RH) sensitivity of charge to changing environmental conditions for toner compositions. While many toners contain silica as a surface additive to provide high charge, silica is known to be RH sensitive. Hence, it is a goal to provide new toner additives that can improve RH sensitivity while maintaining high charge.
Surface additives also suffer from high additive impaction due to the small primary particle size of 7 to 160 nm. While impaction can be reduced by using larger particle sizes, the larger particle sizes cause the additive to be less adhered to the toner surface which can lead to contamination of other surfaces, such as the photoreceptor and BCR.
Thus, there is a need for new surface additives that can provide high charge, low RH sensitivity, and reduced additive impaction with improved adhesion of the additive to the toner surface.